System can't find script to run scheduled operation

For some reason, starting on about April 9, my scheduled backups stopped running.

The scheduled backups start, then, according to the log, terminate with the message "Module Error (Code) 104(0x1006 No such file...../Scripts/6C7EC66D-etc. -etc. " This applies to two separate scheduled operations.

I executed a manual incremental backup without a problem, as well as a trial full backup to the Secure Zone (started then user terminated till later). The only change to the system I can recall from around April 9 is installing the new Microsoft Antispyware program.